The invention relates to a method for modifying a display of a shape, suitable for enabling a user of a CAD system to modify a shape and for providing a display of the modified shape.
In the following, the word &lt;&lt; surface &gt;&gt; will frequently be used. It should be understood in a broad sense and designating a surface properly speaking as well as surface-like piece-wise G.sup.k -continuous defined shape or a &lt;&lt; skin &gt;&gt; of a volume, with k being an integer at least equal to zero, and even presenting some rips (in which case k=-1).
Engineering or styling (aesthetic) requirements may render advisable modifications of a part, or zone, of a pre-existing surface, or even of a whole surface, defined by a topology thereof for making the modified surface passing by locations indicated by a user, such as points or curves with or without tangent planes and normal curvatures fits. Such requirements constitute inner constraints. The modifications should simultaneously respect external constraint: the modified zone must have, within prescribed tolerances, a continuity or smooth transition with the unmodified part of the original surface.
Another problem which may occur in styling or engineering is to generate a display of a curved surface filling a predetermined zone, respecting external constraint along the boundary of the zone and respecting inner constraint. EP-A-0 576 218 discloses a method for solving that problem, which is however limited to obtaining a continuity not exceeding G.sup.1 at the boundaries. That prior art method comprises generating a partial differential equation representing the surface as a physical membrane. That method is not used for modifying a pre-existing shape and does not enable to achieve a higher continuity order at the boundaries.